This commit fixes the module-level docstrings for the tests and helper
modules in qa. Many of these tests were uncommented previously - this
commit ensures that every test case has at least a minimum level of
commenting.
Immature coinbase spends are allowed in the memory pool if they can be mined in the next block.
They are not allowed in the memory pool if they cannot be mined in the next block.
This regression test tests those edge cases.
